• Ball valves are straight-through flow valves which provide positive shutoff with minimal pressure drop and flow turbulence. The barrier to flow is a ball which is rotated 90 degrees to the direction of flow.
• In floating ball valves, the ball has some freedom to move along the axis of the valve while having no freedom to rotate against the stem. when line pressure is applied to the closed ball, it moves slightly (or floats) downstream to maintain contact with the downstream seat where primary sealing occurs.
• Because the stem motion from full open to full closed is a 90 degree rotation, ball valves are ideally suited for automatic operation. they may generally be installed without regard for flow direction.

In three piece ball valves, the ball is held in a fixed axial position by upper and lower stems and can move only in a rotational mode. The resilient seats are contained in metal carriers which are spring loaded against the ball. Line pressure applied to a closed valve increases the spring load on the upstream seat to effect a tight seal. The primary seating is therefore on the upstream seat permitting ball valves to be used for “block and bleed” service.